Question about dictionary sizes.

  • Nobody/Anonymous

    The LZMA algorithm can support up to a 4GB dictionary. Why does 7-zip only allow up to 192 megs, and also, why does it have to be RAM? Why can't it use the pagefile or some form of virtual RAM to compress? I have 1GB of RAM, but a 4GB page file, so I'm limited to the 128MB dictionary size, but I'd like to use more.

    • Nobody/Anonymous

      The GUI lists up to 192MB.  Use the command line options to go further if you really feel the need (max of 2^28=256MB).  Keep in mind that the LZMA algorithm uses an amount of memory that depends on the match finder.  For the most memory efficient matcher (bt2) that means 267 MB.  For pat4h:3181 MB.

      BTW, you really really really do not want to use the virtual memory if you can help it.  Unless you want to wait significant fractions of days to compress anything that would actually benefit from that huge a dictionary.

    • Nobody/Anonymous

      If I'm not mistaken there is no limitation on using virtual memory. It works. Of course, as one would expect it is very very very very very slow and to be honest, IMHO it is a dumb idea to even consider using virtual memory for the dictionary but if you want to do it, you can.


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